Terminal apparatus and base station apparatus

ABSTRACT

A CCA level is made to be variable efficiently while maintaining the fairness relating to acquisition of a transmission opportunity by wireless terminal apparatuses, and thus efficiency of a radio resource is improved. Provided is a terminal apparatus that, performs wireless communication with a base station apparatus, and includes; a MAC frame categorization unit categorizing MAC frames, in each of which media access control header is attached to transmission data, based on a type of MAC frame; and a QoS control unit performing a carrier sense using a first CCA level, in a case where the MAC frame is included in a first category that results from the categorization by the MAC frame categorization unit, and performing the carrier sense using a second CCA level different from the first CCA level, in a case where the MAC frame is included in a second category different from the first category.

The present application is a continuation application of U.S. patentapplication Ser. No. 15/541,843, filed on Jul. 6, 2017, which is theU.S. national phase of International Application No. PCT/JP2016/050040filed Jan. 4, 2016, which designated the U.S. and claims priority toJapanese Patent Application No. 2015-001187 filed in Japan on Jan. 6,2015. The entire disclosure of such parent application is incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a technology of a terminal apparatusand a base station apparatus that control a transmission opportunityusing a carrier sense.

BACKGROUND ART

In recent years, wireless local area network (LAN) has found widepractical application. Building on IEEE 802.11n, which are wireless LANstandards, IEEE 802.11ac standards have been established by theInstitute of Electrical and Electronics Engineers, Inc. (IEEE). Atpresent, standardization activities for IEEE 802.11ax have been startedas a successor to IEEE 802.11n/ac. In 802.11ax Task Group (TG), unlikeconventional wireless LAN standards, an improvement in user throughputper wireless terminal apparatus, as well as an improvement in peakthroughput, is given as a fundamental requirement, in consideration of ascenario that Access Points (AP) or stations (STA) are densely arranged.For the improvement in user throughput, the introduction of ahigh-efficiency simultaneous multiplex transmission scheme (accessscheme) is indispensable.

In standards up to and including IEEE 802.11ac, an access scheme isemployed that is an autonomous distribution control scheme, which isreferred to as Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) as an access scheme. In the CSMA/CA, the opportunity of thewireless terminal apparatus (the AP, the STA, or the like) to performtransmission is temporally divided using a carrier detection processreferred to as a Carrier Sense (CS). For example, the wireless terminalapparatus can determine, using a threshold referred to as the CarrierSense Level, that, in a case where a power higher than a Carrier SenseLevel is detected, the radio resource is busy, and that, in a case whereonly a power lower than the Carrier Sense Level is detected, the radioresource is idle. The Carrier Sense Level is also referred to as a ClearChannel Assessment Level (CCA level), a CCA Threshold, or the like.

For the efficient use of the radio resource, in IEEE 802.11ax TG, asystem has been under study in which every wireless terminal apparatusmakes the CCA level variable based on information (a reception level(Received Signal Strength Indication (RSSI) of a signal received fromthe AP that is connected), the number of times that a transmission erroroccurs, or the like) relating to the reliability of data communication(NPL 1 and NPL 2). If the CCA level is raised, because the opportunityof the wireless terminal apparatus to determine that the radio resourceis busy occurs less frequently, it is considered that the transmissionopportunity (TXOP) can be efficiently ensured even under the environmentwhere the APs or the STAs are densely arranged. Because the raising ofthe CCA level increases the number of wireless terminal apparatuses thatobtains the TXOP in the same radio resource, there is a problem that,the number of interference signals increases, but it is expected thatcommunication quality is maintained with adaptive modulationtransmission or the like.

CITATION LIST Non Patent Literature

NPL 1: IEEE 802.11-14/0779r2

NPL 2: IEEE 802.11-14/0872r0

SUMMARY OF INVENTION Technical Problem

However, in a case where a system in which every wireless terminalapparatus changes the CCA level is used, the wireless terminal apparatusthat has high reliability of the data transmission can acquire thetransmission opportunity more frequently because the CCA level can beraised. On the other hand, the wireless terminal apparatus that has lowreliability of the data transmission takes the transmission opportunityless frequently because the CCA level is difficult to raise. As aresult, there is a likelihood that the number of wireless terminalapparatuses that have low user throughput will increase.

An object of the present invention, which is made in view of thesituation described above, is to provide a terminal apparatus and a basestation apparatus that are capable of improving efficiency of a radioresource by efficiently making a CCA level variable while maintainingthe fairness relating to acquisition of opportunities of wirelessterminal apparatuses to perform transmission.

Solution to Problem

To accomplish the object described above, the present invention iscontrived to provide the following means. That is, according to thepresent invention, there is provided a terminal apparatus that findsapplication in a communication system which controls a transmissionopportunity using a carrier sense, and that performs wirelesscommunication with a base station apparatus. The terminal apparatusincludes; a MAC frame categorization unit that categorizes MAC framesusing a MAC frame categorization information for categorizing the MACframes, and a QoS control unit that performs a carrier sense, for everycategory, on the MAC frame that results from the categorization. The QoScontrol unit changes a CCA level of the carrier sense performed forevery category, based on first clear channel assessment (CCA) indicationinformation obtained from the base station apparatus.

In this manner, the MAC frames are categorized using the MAC framecategorization information for categorizing the MAC frames, and the CCAlevel of the carrier sense performed for every category is changed basedon first CCA indication information acquired from the base stationapparatus, when the carrier sense is performed, for every category, onthe MAC frame that results from the categorization. Because of this, itis possible that the CCA level is made to be variable efficiently whilemaintaining the fairness relating to acquisition of opportunities ofterminal apparatuses to perform transmission.

As a result, it is possible that efficiency of a radio resource isimproved.

Advantageous Effects of Invention

According to the present invention, it is possible that a CCA level ismade to be variable efficiently while maintaining the fairness relatingto acquisition of opportunities of wireless terminal apparatuses toperform transmission. As a result, the efficiency of the radio resourceis improved, and it is possible that user throughput is greatlyimproved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating an example of a communicationsystem according to a first embodiment.

FIG. 2 is a schematic diagram illustrating an example of an aspect ofcommunication in a system in compliance with IEEE 802.11, which performsthe communication based on CSMA/CA.

FIG. 3 is a table illustrating an example of a correspondence betweeneach AC and a parameter.

FIG. 4 is a schematic diagram illustrating an example of operationrelating to QoS of a STA 2 according to the present embodiment.

FIG. 5 is a block diagram illustrating an example of a constitution ofthe STA 2 according to the present embodiment.

FIG. 6 is a diagram illustrating an example of a MAC frame generated bya higher layer unit 201.

FIG. 7 is a block diagram illustrating an example of a constitution ofan AP 1 according to the present embodiment.

FIG. 8 is a diagram illustrating an example of an EDCA parameternotified by the AP 1 according to the present embodiment.

FIG. 9 is a schematic diagram of an example of operation of a QoScontrol unit 2022 in the STA 2.

FIG. 10 is a diagram that schematically illustrates a communicationsystem according to a second embodiment.

FIG. 11 is a block diagram illustrating an example of a constitution ofan AP 21 according to the present embodiment.

FIG. 12 is a block diagram illustrating an example of a constitution ofa STA 22 according to the present embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

A communication according to the present embodiment includes an AccessPoint (AP) that preforms wireless transmission and wireless reception,or a station (STA) that performs the wireless transmission and thewireless reception, or the AP and the STA. Furthermore, a network thathas the AP, the STA, or the AP and the STP is referred to as a basicservice set (BSS).

FIG. 1 is a schematic diagram illustrating an example of a communicationsystem according to a first embodiment of the present invention. Thecommunication system in FIG. 1 includes an AP 1, STAs 2-1 to 2-3, and aBSS 1 a. The BSS 1 a has the AP 1 and the STAs 2-1 to 2-3. The STAs 2-1to 2-3 is hereinafter simply referred to as a STA 2.

The AP 1 and the STA 2 each are assumed to perform communication basedon carrier sense multiple access with collision avoidance (CSMA/CA). Inthe present embodiment, an infrastructure mode in which the STA 2 andthe AP 1 perform communication is intended, but a method according tothe present embodiment is capable of being implemented also in an ad hocmode in which the STAs 2 directly perform communication.

FIG. 2 is a diagram illustrating an example of an aspect ofcommunication in a system in compliance with IEEE 802.11, which performsthe communication based on the CSMA/CA. In FIG. 2, as an example, uplink(UL) communication is assumed to be performed, but in the methodaccording to the present embodiment, downlink (DL) communication may bepossible. The STA 2 performs a Carrier Sense (CS) based on the CSMA/CA,and thus determines a state of a radio resource.

Specifically, in a case where a power higher than a Carrier Sense Levelis detected using a threshold referred to as the Carrier Sense Level,the radio resource can be determined as being busy, and in a case whereonly a power lower than the Carrier Sense Level is detected, the radioresource can be determined as being idle. The Carrier Sense Level isalso referred to as a Clear Channel Assessment Level (CCA level) or aCCA Threshold. In an example in FIG. 2, the STA 2 is changed from busyto idle, and transmission preparation is started. First, as a firststage of the transmission preparation, the STA 2 performs the CarrierSense only for a waiting time (Interframe Space (IFS)) that isconfigured in advance and determines the state of the radio resource.

In FIG. 2, as the waiting time, a Distributed IFS (DIFS) is configured.As the IFS, in addition, there are a Short IFS used for transmission ofa transmission frame that has a high priority level, such as anacknowledgment (Ack), an Extended IFS (EIFS) that is used such as whenthe radio resource is determined as being busy, but the frame isdifficult to receive correctly, and the like. Furthermore, in IEEE802.11e, there is an Attribution IFS (AIFS) that varies in a manner thatcorresponds to a priority level which is based on a category (AccessCategory (AC)) of the transmission frame introduced for improvement inQuality of Service (QoS). The QoS and the AIFS will be described below.

The STA 2 waits only the IFS configured in advance, and then proceeds toa backoff. In the backoff, each STA 2 causes a random value to occur,and waits only as much waiting time (Slot Time) as random value×1 slotfor transmission. The waiting time that occurs randomly is also referredto as a Contention Window (CW). The AP 1 instructs each STA 2 that makesa connection, on an upper limit value (CW max) and a lower limit value(CW min) of the random value that each STA 2 causes to occur. In a casewhere there is no instruction from the AP 1, the STA 2 depends oninformation retained within the STA 2 itself, or configures an initialvalue. Furthermore, a specific value (User Priority (UP)) configured forevery transmission frame for the purpose of QoS control can beconfigured for a CW max and a CW min. The STAs 2 have different CW's,and thus collisions among data frames can be efficiency avoided.

In the example in FIG. 2, because the STA 2-1 has the shortest CW, theSTA 2-1 is the first to acquire a transmission opportunity, and cantransmit data to the AP 1 that is connected. Furthermore, when the STA2-1 completed data transmission, the remaining STAs 2-2 and 2-3 eachwait the DIFS and only the rest of the CW, and the STA 2-2 that waitsthe rest of the CW which is shorter acquires a transmission opportunity.It is noted that, also while the CW counts down, the STA 2 performs theCarrier Sense, and when the radio resource is determined as being busy,the CW stops counting down.

In IEEE 802.11e, priority level control that is based on the AC isstipulated for the purpose of an improvement in QoS. FIG. 3 is a tableillustrating an example of a correspondence between each AC and aparameter. The AC and a name (Designation) thereof are configured foreach UP, and an Enhanced Distributed Channel Access parameter (EDCAparameter) is configured in order of increasing the priority level, thatis, in this order: AC_VO, AC_VI, AC_BE, AC_BK. The EDCA parametersinclude parameters that are used when accessing the radio resource, suchas a length of the AIFS, a CW min, and a CW max. The EDCA parameter isconfigured for every AC, and thus it is possible that the QoS isimproved.

The EDCA parameter used for the QoS can be notified by the AP 1 to theSTA 2, using a broadcast signal (beacon). Furthermore, in a case wherethe EDCA parameter is notified by the AP 1, an EDCA parameter (defaultEDCA parameter set) that is configured in advance for the STA 2 can beused.

FIG. 4 is a schematic diagram illustrating an example of operationrelating to QoS of the STA 2 according to the present embodiment. TheSTA 2 categories a group of pieces of transmission data on whichprioritization is performed, for every AC. The STA 2 waits only the AIFSthat corresponds to the AC, configures each backoff, and operates as ifcontention occurs within the terminal. At this point, AIFS[ACx]indicates a value of the AIFS when the AC is ACx. With the use of AC_VIin which the AC has the highest priority level, AIFS[AC_VI] is used, andproceeding to the backoff takes place most quickly.

Next, the random value is caused to occur based on values of CW min andCW max, and the CW is configured. At this time, it is considered that,with the use of AC_VI that has the highest priority level, the smallestCW min and CW max are configured, but because the random value is used,there is also a case where a size of the CW is no smaller than that ofthe CW configured with the use of another AC.

In an example in FIG. 4, AC_VI acquires a transmission opportunity, andsubsequently, AC_VO acquires a transmission opportunity. AC_VO or AC_VIin which the AIFS is configured to be short acquires a transmissionopportunity with ease, and AC_BE or AC_BK in which the AIFS isconfigured to be long acquires a transmission opportunity withdifficulty.

FIG. 5 is a block diagram illustrating an example of a constitution ofthe STA 2 according to the present embodiment. As illustrated in FIG. 5,the STA 2 has a higher layer unit 201, a control unit 202, atransmission unit 203, a reception unit 204, and an antenna unit 205.

The higher layer unit 201 sends a MAC frame in which a Media AccessControl (MAC) header is attached to transmission data, and a value ofthe AC, which is associated with the MAC frame, to the control unit 202.Furthermore, demodulation data obtained by the control unit 202 from thereception unit 204 is sent to the higher layer unit 201, andretransmission and the like are performed by a media access controllayer and Logical Link Control (LLC) that are included in the higherlayer unit 201.

FIG. 6 is a diagram illustrating an example of the MAC frame generatedby the higher layer unit 201. A frame control subfield is used fordetermination of a transmission type or for fragment control. A QoScontrol subfield is used for notifying information (a Traffic Identifier(TID)) relating to the QoS.

The STA 2 according to the present embodiment, for example, may notifyinformation relating to the QoS or information a CCA level, for example,with the QoS control subfield. Furthermore, notification means is notlimited to this. As the notification means, other subfields or a fieldwithin a header (a Physical Layer Convergence Protocol header (PLCPheader), a PHY header, or the like) relating to a physical layer (PHYlayer) attached to the MAC frame with the use of the physical layer maybe used, and a portion of the transmission data may be used. A framebody is sent from the higher layer unit 201 and expresses thetransmission data. A Frame Check Sequence (FCS) field is used fordetection of an error in the MAC frame.

In FIG. 5, the control unit 202 has a MAC frame categorization unit 2021and a QoS control unit 2022. The MAC frame categorization unit 2021, forexample, categorizes the MAC frames that are sent from the higher layerunit 201, for every AC, using a value of the AC associated with the MACframe. The post-categorization MAC frame is sent to the QoS control unit2022.

It is noted that operation of the MAC frame categorization unit 2021 isnot limited to what is described above. For example, the MAC framecategorization unit 2021 can perform categorization according to areference that is based on the number of times that the MAC frame isretransmitted. Specifically, the MAC frame categorization unit 2021 cancategorize the MAC frame according to a size of value of a retry count,with reference to information (a Short Retry Count (SRC) or a Long RetryCount (LRC) (the SRC and the LRC are hereinafter collectively referredto as the retry count) relating to the number of times associated withthe MAC frame.

Furthermore, the MAC frame categorization unit 2021 can categorize theMAC frames according to a size of information (a data size, an amount ofinformation, a payload size, a frame length, a data length, or the like)relating to a size of the MAC frame. Furthermore, in addition, the MACframe categorization unit 2021 may categorize radio resources and maycategorize MAC frames according to the number of multiplex frames.

An example of a case where the MAC frame categorization unit 2021performs the categorization according to the AC of the MAC frame will bedescribed below, but the present embodiment is not limited to this.Information used by the MAC frame categorization unit 2021 forcategorizing the MAC frame is referred to as MAC frame separationinformation.

The QoS control unit 2022 retains the post-categorization MAC frame,which is sent from the MAC frame categorization unit 2021, performsautonomous distribution control that is based on the CSMA/CA, for everyAC or for every category that results from performance by the MAC framecategorization unit 2021, and sends the MAC frame, that gains atransmission opportunity, to a physical channel signal generation unit2031. Operation of the QoS control unit 2022 will be in detail below.

The transmission unit 203 has the physical channel signal generationunit 2031 and a wireless transmission unit 2032.

The physical channel signal generation unit 2031 converts thetransmission data sent from the QoS control unit 2022, into a physicalchannel signal (baseband signal). Furthermore, the physical channelsignal generation unit 2031 converts a Training Field (TF) used forchannel estimation, into the physical channel signal. The physicalchannel signal generation unit 2031 multiplexes the physical channelsignal generated from the MAC frame, and the TF, and generates thetransmission frame. Physical channel signal conversion processingperformed by the physical channel signal generation unit 2031 includeserror correction coding, mapping, and the like.

The wireless transmission unit 2032 performs processing that convertsthe transmission frame generated by the physical channel signalgeneration unit 2031 into a signal in a Radio Frequency (RF) band.Processing performed by the wireless transmission unit 2032 includesdigital-to-analog conversion, filtering, frequency conversion from abaseband to a RF band, and the like.

The reception unit 204 demodulates a signal in the RF band, which isreceived by the antenna unit 205. The reception unit 204 has a wirelessreception unit 2041 and a physical channel signal demodulation unit2042.

The wireless reception unit 2041 converts the signal in the RF bandreceived by the antenna unit 205, into the physical channel signal.Processing performed by the wireless reception unit 2041 includesprocessing for conversion from the RF band to the baseband, filtering,and analog-to-digital conversion. Furthermore, the wireless receptionunit 2041 obtains information associated with a received power of thesignal in the RF band, which is received by the antenna unit 205.Information associated with the received power is sent to the controlunit 202, a comparison with the CCA level is made in the QoS controlunit 2022, and a determination of whether the radio resource is busy oridle is made.

The physical channel signal demodulation unit 2042 performs channelequalization, demapping, error correction decoding processing, and thelike on the physical channel signal generated by the wireless receptionunit 2041, and generates the demodulation data. The demodulation data issent to the control unit 202, and then is sent to the higher layer unit201.

The antenna unit 205 transmits the signal in the RF band, which is sentfrom the wireless transmission unit 2032, to a wireless space, in stateof being destined for the STA 2. Furthermore, the signal in the RF band,which is transmitted from the STA 2, is received by the wireless space.

FIG. 7 is a block diagram illustrating an example of a constitution ofthe AP 1 according to the present embodiment. The AP 1 has a higherlayer unit 101, a control unit 102, a transmission unit 103, a receptionunit 104, and an antenna unit 105.

The higher layer unit 101 attaches a MAC header to the transmission datafrom a higher layer, and thus generates the MAC frame. Furthermore, thecontrol unit 102 processes the MAC frame sent from the control unit 102.

The control unit 102 has a MAC frame categorization unit 1021 and a QoScontrol unit 1022. The MAC frame categorization unit categorizes the MACframes based on the MAC frame separation information. For example, theMAC frames are categorized based on the MAC frame sent from the higherlayer unit 101, and the value of the AC associated with the MAC frame.

The QoS control unit 1022 retains the post-categorization MAC frame,which is sent from the MAC frame categorization unit 1021, performs theautonomous distribution control that is based on the CSMA/CA, for everyAC or for every category that results from performance by the MAC framecategorization unit 1021, and sends the MAC frame that gains atransmission opportunity, to a physical channel signal generation unit1031. Operation of the QoS control unit 1022 will be in detail below.

The transmission unit 103 has the physical channel signal generationunit 1031, a broadcast signal generation unit 1032, and a wirelesstransmission unit 1033. The physical channel signal generation unit 1031converts the transmission data sent from the QoS control unit 1022, intothe physical channel signal (baseband signal). Furthermore, the physicalchannel signal generation unit 1031 also converts the TF used for thechannel estimation, into the physical channel signal. The physicalchannel signal generation unit 1031 multiplexes the physical channelsignal generated from the MAC frame, and the TF, and generates thetransmission frame. The physical channel signal conversion processingperformed by the physical channel signal generation unit 1031 includesthe error correction coding, the mapping, and the like.

The broadcast signal generation unit 1032 generates the broadcastsignal. The generated broadcast signal is converted into the physicalchannel signal, and is sent to the wireless transmission unit 1033. Thebroadcast signal can include information elements, such as a BeaconInterval (broadcast signal interval), Supported Rates, a PowerConstraint, a Transmit Power Control Report (TPC report), an EDCAparameter, and a QoS Capability information element. The Beacon Intervalis an information element used to notify the STA 2, which connects tothe AP 1, of an interval at which the broadcast signal is notified. TheSupported Rates are information elements that are used to notify the STA2 of a data rate (a coding rate or a transmission rate given by amodulation scheme) which is supported by the AP 1 (or a BSS 1 a).

The Power Constraint is an information element used for the AP 1 tonotify the STA 2 of information relating to a transmit power. The TPCReport is an information element used for the AP 1 to notify the STA 2of information relating to TPC. The EDCA parameter is an informationelement used for the AP 1 to notify the STA 2 of information relating tothe EDCA parameter.

FIG. 8 is a diagram illustrating an example of the EDCA parameternotified by the AP 1 according to the present embodiment. The AP 1 cannotify the STA 2 of first CCA indication information indicating a changeof a CCA level of the STA 2, in a state of being added to theinformation relating to the EDCA parameter. The AP 1 may use a CCAOffset, as the first CCA indication information, which explicitlyindicates a change value of the CCA level of the STA 2. Operation of theSTA 2 that is performed when the first CCA indication information isnotified will be described in detail below. It is noted that a method inwhich the AP 1 notifies the first CCA indication information is notlimited to this, and that the first CCA indication information may beadded to a PHY header (a physical header or a PLCP header) and beinserted into the transmission data.

A CWmin and a CWmax are values that are decided in advance within theterminal or the BSS, in compliance with IEEE 802.11 standards. The STA 2generates a CW of each AC, using a CWmin, a CWmax, or both that areincluded in the EDCA parameter that is broadcast from the AP 1. An AIFSNis a parameter used for the STA 2 to calculate the AIFS. AIFS[ACx]relating to a value ACx of the AC, for example, is calculated byEquation (1).

AIFS[ACx]*AIFSN[ACx]*aSlotTime+aSIFSTime   (1)

In Equation (1), aSlotTime is a value of Slot Time configured in advancewithin the STA 2 or the BSS 1a, or in compliance with IEEE 802.11standards. Furthermore, aSIFSTime is a value of the SIFS configured inadvance within the STA 2 or the BSS 1 a, or in compliance with IEEE802.11 standards. The QoS control unit 2022 of the STA 2 performs theautonomous distribution control that is based on the CSMA/CA, for everyAC, using the value of the AIFS demanded by Equation (1).

The AP 1 according to the present embodiment, for example, can add thefirst CCA indication information to a portion of the broadcast signalgenerated by the broadcast signal generation unit 1032, a portion of theEDCA parameter that is an information element, or portions of otherinformation elements. The AP 1 converts the broadcast signal generatedby the broadcast signal generation unit 1032, into an RF signal, andtransmits the resulting RF signal in a state of being destined for theSTA 2, using the antenna unit 105. The STA 2 receives the broadcastsignal transmitted by the antenna unit 105, and performs receptionprocessing, using the reception unit 204. The MAC frame that goesthrough the reception processing is sent to the higher layer unit 201,and the first CCA indication information that is present within thebroadcast signal is obtained. The higher layer unit 201 instructs theQoS control unit 2022 to cause the CCA level to be variable, using theacquired first indication information.

CCA Offset in FIG. 8 indicates an offset value of the CCA level in eachAC of the STA 2. If a value of CCA Offset is assumed to be Co, a valueof the CCA level of the STA 2 is assumed to be Cd, CCA level Ce used bySTA 2 is calculated using Equation (2).

Ce=Cd+Co   (2)

It is noted that CCA Offset is not limited to a value in FIG. 8, and maynot be a value decided in advance. The AP 1 may cause CCA Offset to bechanged for every STA 2, and may cause CCA Offset to be temporallychanged.

For example, the AP 1 can decide CCA Offset in such a manner that a CCAlevel of the AC that has a high priority level is raised and a CCA levelof the AC that has a low priority level is lowered. For example, CCAOffset is configured as described above, and thus it is possible that agreat transmission opportunity is given the MAC frame of the AC that hasa high priority. However, a method of deciding CCA Offset of the AP 1according to the present embodiment is not limited to this. A method ofdeciding CCA Offset in such a manner that the CCA level of the AC thathas a high priority level is lowered may be employed, and CCA Offset maybe decided using other methods.

It is noted that the first CCA indication information may not be CCAOffset, and may be information associated with CCA Offset. Furthermore,instead of CCA Offset, the first CCA indication information may beinformation associated with a value for directly designating the CCAlevel used by the STA 2, and may be information associated with a methodof calculating the CCA level used by the STA 2.

The QoS Capability in the broadcast signal is an information element fornotifying the STA 2 of information associated with the acceptability andnon-acceptability of the QoS.

The AP 1 according to the present embodiment may notify the STA 2 of thefirst CCA indication information using an information element other thanthe EDCA parameter that is an information element. Furthermore, a methodof notifying the first CCA indication information is not limited tothis, and the first CCS indication information may be included in theMAC header, a PLCP header, or the transmission data.

The wireless transmission unit 1033 performs processing that convertsthe transmission frame and the broadcast signal that are sent by thephysical channel signal generation unit 1031 or the broadcast signalgeneration unit 1032, into the signal in the RF band. Processingperformed by the wireless transmission unit 1033 includes thedigital-to-analog conversion, the filtering, the frequency conversionfrom the baseband to the RF band, and the like.

The reception unit 104 has a wireless reception unit 1041 and a physicalchannel signal demodulation unit 1042. The wireless reception unit 1041converts the signal in the RF band received by the antenna unit 105,into the physical channel signal. Processing performed by the wirelessreception unit 1041 includes processing (processing for conversion tothe physical channel signal) for frequency conversion from the RF bandto the baseband, the filtering, and the analog-to-digital conversion.Furthermore, the wireless reception unit 1041 obtains informationassociated with the received power of the signal in the RF band, whichis received by the antenna unit 105. Information associated with thereceived power is sent to the control unit 102, the comparison with theCCA level, is made in the QoS control unit 1022, and thus thedetermination of whether the radio resource is busy or idle is made.

The physical channel signal demodulation unit 1042 performs the channelequalization, the demapping, the error correction decoding processing,and the like on the physical channel signal generated by the wirelessreception unit 1041, and generates the demodulation data. Thedemodulation data is sent to the control unit 102, and then is sent tothe higher layer unit 101.

The antenna unit 105 transmits the signal in the RF band, which is sentfrom the wireless transmission unit 1033, to the wireless space, instate of being destined for the STA 2. Furthermore, the signal in the RFband, which is transmitted from the STA 2, is received by the wirelessspace.

FIG. 9 is a schematic diagram of an example of the QoS control unit 2022in the STA 2. A transmission queue that corresponds to each of the AC'sretains the MAC frame categorized by the MAC frame categorization unit2021. The autonomous distribution control that is based on the CSMA/CAfor every AC, a correspondence to which is established is performed onthe retained MAC frame. The autonomous distribution control that isbased on the CSMA/CA includes a transmission waiting operation and abackoff operation, in which the STA 2 waits only the AIFS or an IFSother than the AIFS for the transmission of the MAC frame. Based on theCCA indication information notified by the AP 1, the STA 2 generates theCW relating to the backoff for the MAC frame that corresponds to each ofthe AC's. The STA 2 sends one MAC frame selected by a collisionavoidance mechanism, to the transmission unit.

It is noted that the STA 2 may configure the CCA level that correspondsto each of the AC's, based on second CCA indication informationretained, by the STA 2, within the STA 2 itself (in a memory, storage, adatabase, or the like), without depending on the first CCA indicationinformation that is broadcast from the AP 1. Furthermore, the STA 2 maycreate third CCA indication information from information other than theEDCA parameter from the AP 1. For the creation of the third CCAindication information, the STA 2 may perform the categorization of thetransmission frames by a type of transmission frame, and may change theCCA level for every transmission frame group that results from thecategorization. Furthermore, because the present embodiment is alsoapplicable to downlink transmission, it is possible that like the STA 2,the AP 1 also changes the CCA level according to each of the AC's or acategory other than the AC, based on the first CCA indicationinformation, the second CCA indication information, and the third CCAindication information.

With the AP 1 and the STA 2, which are described above, the CCA level ismade to be variable based on the first CCA indication information, thesecond CCA indication information, or the third CCA indicationinformation, which is retained by the STA 2, and thus a mechanism inwhich the CCA level is made to be effectively variable can be introducedand the radio resource can be efficiently used while maintaining thefairness relating to the acquisition of the transmission opportunitiesby the wireless terminal apparatuses. Because of this, it is possiblethat user throughput is greatly improved.

Second Embodiment

FIG. 10 is a diagram that schematically illustrates a communicationsystem according to a second embodiment. The communication systemillustrated in FIG. 10 includes an AP 21, STAs 22-1, 22-2, and STAs 23-1and 23-2, and a BSS 2 a. The BSS 2 a includes the AP 21, the STAs 22-1and 22-2, and the STAs 23-1 and 23-2. The STAs 22-1 and 22-2 are STAsthat can make the CCA level variable, and the STAs 23-1 and 23-2 areterminals that have difficulty in making the CCA level variable. TheSTAs 22-1 and 22-2 and the STAs 23-1 and 23-2 will be described below ascorresponding to the QoS, but the STAs 23-1 and 23-2 may not ensure theQoS. The STAs 22-1 and 22-2 and the STAs 23-1 and 23-2 are hereinafteralso referred to as a STA 22 and a STA 23, respectively.

The AP 21, the STA 22, and the STA 23 each are assumed to performcommunication based on the CSMA/CA. In the present embodiment, aninfrastructure mode in which the STA 22, the STA 23, and the AP 21perform the communication is intended, but a method according to thepresent embodiment is capable of being implemented also in the ad hocmode in which the STAs 2 directly perform the communication. It is notedthat operation of the CSMA/CA is the same as in the first embodimentunless specified otherwise.

FIG. 11 is a block diagram illustrating an example of a constitution ofthe AP 21 according to the present embodiment. As illustrated in FIG.11, a higher layer unit 2101, a control unit 2102, a transmission unit2103, a reception unit 2104, and an antenna unit 2105 are included. Thecontrol unit 2102 includes a MAC frame categorization unit 21021 and aQoS control unit 21022. The transmission unit 2103 includes a physicalchannel signal generation unit 21031 and a wireless transmission unit21032. The reception unit 2104 includes a wireless reception unit 21041and a physical channel signal demodulation unit 21042.

A comparison between the AP 21 and the AP 1 according to the firstembodiment shows that the AP 21 has the broadcast signal generation unit21032 different from the broadcast signal generation unit 21032 of theAP 1. However, in terms of the other constitutions, because functionsthat are the same as those according to the first embodiment areretained, descriptions thereof are omitted.

A broadcast signal generation unit 21032 generates the broadcast signal.The generated broadcast signal is converted into the physical channelsignal, and is sent to a wireless transmission unit 21033. The broadcastsignal can include information elements, such as the Beaon Inteval, theSupported Rates, the Power Constraint, the TPC Report, the EDCAparameter, and the QoS Capability information element.

The AP 21 according to the present embodiment has the feature ofnotifying information relating to a plurality of EDCA parameters throughthe broadcast signal generated by the broadcast signal generation unit.For example, the AP 21 can notify the STA 22 and the STA 23 of an EDCAparameter (axEDCA) for the STA 22 and an EDCA parameter (legacy EDCA)for the STA 23, respectively. For example, the AP 21 can add the firstCCA indication information or the third CCA indication information tothe axEDCA.

For example, the AP 21 can make a value of the AIFSN in the axEDCAgreater than a value of the AIFSN in the legacy EDCA. Therefore, atransmission waiting time AIFS for the STA 23 is shorter than the AIFSfor the STA 22. With the operation described above, the STA 22 makes theCCA variable and thus it is possible that the STA 23 is protected fromthe unfairness of a transmission opportunity acquisition rate to the STA22 and the STA 23. It is noted that the AP 21 may change an EDCAparameter other than the AIFSN for the protection of the STA 23.Furthermore, the AP 21 may notify the STA 22 and the STA 23 of theaxEDCA and the legacy EDCA for a purpose other than the protection ofthe STA 23.

FIG. 12 is a block diagram illustrating an example of a constitution ofthe STA 22 according to the present embodiment. As illustrated in FIG.12, the STA 22 includes a higher layer unit 2201, a control unit 2202, atransmission unit 2203, a reception unit 2204, and an antenna unit 2205.The control unit 2202 includes a MAC frame categorization unit 22021 anda QoS control unit 22022. The transmission unit 22031 includes aphysical channel signal generation unit 2203 and a wireless transmissionunit 22032. The reception unit. 2204 includes a wireless reception unit22041 and a physical channel signal demodulation unit 22042.

A comparison between the STA 22 and the STA 2 according to the firstembodiment shows that the STA 22 has the QoS control unit 22022different from the QoS control unit 22022 of the STA 2. However, interms of the ether constitutions, because functions that are the same asthose according to the first embodiment are retained, descriptionsthereof are omitted.

The QoS control unit 22022 retains the post-categorization MAC frame,which is sent from the MAC frame categorization unit 22021, performs theautonomous distribution control that is based on the CSMA/CA, on everyAC or on every category that results from performance by the MAC framecategorization unit 22021, and sends the MAC frame that gains atransmission opportunity, to the physical channel signal generation unit22031. The QoS control unit 22022 obtains axEDCA information in abroadcast signal of the AP 21, and can make the CCA level variable basedon the first CCA indication information or the third CCA indicationinformation In a case where the first CCA indication information fromthe axEDCA information, or the third CCA indication information isdifficult to obtain, the QoS control unit 22022 can make the CCA levelvariable based on the second CCA indication information within the STA22.

The STA 22 according to the present embodiment can obtain the axEDCAthat is broadcast by the AP 21, and information relating to two types ofEDCA parameters of the legacy EDCA, and can calculate CCA Offset fromthe axEDCA and the legacy EDCA.

The STA 22 will be described below as calculating CCA Offset from theaxEDCA, and from information relating to the AIFSN of the legacy EDCA,but CCA Offset may be calculated using a parameter other than the AIFSNin the EDCA parameter.

A value of the AIFSN written to the axEDCA is assumed to be Nax, and avalue of the AIFSN written to the legacy EDCA is assumed to be N1.Because the value of the AIFSN is configured for every AC, for example,configurations are assumed to be provided such as Nax=[7, 3, 2, 2] andN1=[4, 2, 1, 1], and AIFSN's of AC_BK, AC_BE, AC_VO, and AC_VI areassumed to be expressed starting from the first term. A Value Ca1 of CCAOffset is calculated using Equation (3).

Cal=α*(Nax−Nl)   (3).

In Equation (3), α is a coefficient for calculating CCA Offset, and is avalue retained in information notified by the AP 21 or in a databasewithin the STA 22. Furthermore, a method of calculating CCA Offset isalso a value retained in the information notified by the AP 21 and inthe database within the STA 22. Information relating to the method ofcalculating the CCA is hereinafter also referred to as fourth CCAindication information. It is noted that the fourth CCA indicationinformation is not limited to Equation (3), and other equations forcalculation can be used.

The STA 23 is different from the STA 22 in that it is difficult to makethe CCA variable. However, in terms of the other constitutions, becausefunctions that are the same as those of the STA 22 are retained,descriptions thereof are omitted.

The STA 22 performs a QoS operation using the legacy EDCA that isbroadcast, by the AP 21. Because the legacy EDCA has a value differentfrom the axEDCA, it is possible that the STA 23 and the STA 22 realizedifferent QoS operations.

(1) A terminal apparatus according to the present embodiment is alsocapable of having the following aspects. That is, according to thepresent embodiment, there is provided a terminal apparatus that findsapplication in a communication system which controls a transmissionopportunity using a carrier sense, and that performs wirelesscommunication with a base station apparatus, the terminal apparatusincluding; a MAC frame categorization unit that categorizes MAC framesusing a MAC frame categorization information for categorizing the MACframes, and a QoS control unit that performs a carrier sense, for everycategory, on the MAC frame that results from the categorization, inwhich the QoS control unit changes a CCA level of the carrier senseperformed for every category, based on first clear channel assessment(CCA) indication information obtained from the base station apparatus.

(2) Furthermore, in the terminal apparatus according to the presentembodiment, the QoS control unit changes the CCA level of the carriersense performed for every category, based on second CCA indicationinformation retained by the terminal apparatus itself, instead of on thefirst CCA indication information.

(3) Furthermore, in the terminal apparatus according to the presentembodiment, the first CCA indication information is included in anEnhanced Distributed Channel Access (EDCA) parameter.

(4) Furthermore, the terminal apparatus according to the presentembodiment obtains third CCA indication information included inbroadcast information other than the EDCA parameter, from the basestation apparatus, and changes the CCA level of the carrier senseperformed for every category, based on the third CCA indicationinformation, instead of on the first CCA indication information.

(5) Furthermore, the terminal apparatus according to the presentembodiment calculates fourth CCA indication information from informationrelating to a plurality of EDCA parameters that are broadcast by thebase station apparatus, and makes CCA variable using the fourth CCAindication information.

(6) Furthermore, according to the present embodiment, there is proved abase station apparatus that finds application in a communication systemwhich controls a transmission opportunity using a carrier sense, andperforms wireless communication with at least one terminal apparatus,the base station apparatus including a control unit that generates firstCCA indication information that indicates a Clear Channel AssessmentLevel (CCA) Level of the carrier sense performed, for every category, onthe MAC frame that results from the categorization, in the terminalapparatus, and a wireless transmission unit that notifies the terminalapparatus of the first CCA information.

(7) Furthermore, in the base station apparatus according to the presentembodiment, the first CCA indication information is information relatingto a CCA level with which the terminal apparatus complies, or a methodof calculating the information relating to the CCA level with which theterminal apparatus complies.

(8) Furthermore, in the base station apparatus according to the presentembodiment, the first CCA indication information is included in abroadcast signal that is broadcast by the base station apparatus, a MACheader attached by a higher layer to transmission data, a PHY headerattached by a physical channel signal generation unit to the MAC frame,or in a data frame.

(9) Furthermore, according to the present embodiment, there is provideda base station apparatus including a MAC frame categorization unit thatcategorizes MAC frames based on MAC frame information, and a QoS controlunit that performs the carrier sense performed, for every category, onthe MAC frame, using the MAC frame categorization information, in whichthe CCA level is calculated based on the second CCA indicationinformation, a CCA level is changed when performing the carrier sense,for every category, on the MAC frame using the MAC frame categorizationinformation.

(10) Furthermore, in the base station apparatus according to the presentembodiment notifies the terminal apparatus of information relating tothe plurality of EDCA parameters.

As described above, with the AP 21, the STA 22, and the STA 23 accordingto the present embodiment, each of a terminal in compliance with802.11ax and a legacy terminal can be caused to perform different QoSoperations using information relating to two types of EDCA parameters,the axEDCA and the legacy EDCA, and while the terminal in compliancewith 802.11ax greatly improves throughput with the variability of theCCA level, it is also possible that the legacy terminal is protectedfrom a decrease in throughput.

Moreover, the present international application claims the benefits ofJapanese Patent Application No. 2015-001187 filed on Jan. 6, 2015, andthe entire contents of Japanese Patent Application No. 2015-001187 areincorporated herein by reference.

REFERENCE SIGNS LIST

1 AP

2-1 to 2-3 STA

101 HIGHER LAYER UNIT

102 CONTROL UNIT

103 TRANSMISSION UNIT

104 RECEPTION UNIT

105 ANTENNA UNIT

201 HIGHER LAYER UNIT

202 CONTROL UNIT

203 TRANSMISSION UNIT

204 RECEPTION UNIT

205 ANTENNA UNIT

1021 MAC FRAME CATEGORIZATION UNIT

1022 QoS CONTROL UNIT

1031 PHYSICAL CHANNEL SIGNAL GENERATION UNIT

1032 BROADCAST SIGNAL GENERATION UNIT

1033 WIRELESS TRANSMISSION UNIT

1041 WIRELESS RECEPTION UNIT

1042 PHYSICAL CHANNEL SIGNAL DEMODULATION UNIT

2021 MAC FRAME CATEGORIZATION UNIT

2022 QoS CONTROL UNIT

2031 PHYSICAL CHANNEL SIGNAL GENERATION UNIT

2032 WIRELESS TRANSMISSION UNIT

2041 WIRELESS RECEPTION UNIT

2042 PHYSICAL CHANNEL SIGNAL DEMODULATION UNIT

2101 HIGHER LAYER UNIT

2102 CONTROL UNIT

2103 TRANSMISSION UNIT

2104 RECEPTION UNIT

2105 ANTENNA UNIT

2201 HIGHER LAYER UNIT

2202 CONTROL UNIT

2203 TRANSMISSION UNIT

2204 RECEPTION UNIT

2205 ANTENNA UNIT

21021 MAC FRAME CATEGORIZATION UNIT

21022 QoS CONTROL UNIT

21031 PHYSICAL CHANNEL SIGNAL GENERATION UNIT

21032 BROADCAST SIGNAL GENERATION UNIT

21033 WIRELESS TRANSMISSION UNIT

21041 WIRELESS RECEPTION UNIT

21042 PHYSICAL CHANNEL SIGNAL DEMODULATION UNIT

22021 MAC FRAME CATEGORIZATION UNIT

22022 QoS CONTROL UNIT

22031 PHYSICAL CHANNEL SIGNAL GENERATION UNIT

22032 WIRELESS TRANSMISSION UNIT

22041 WIRELESS RECEPTION UNIT

22042 PHYSICAL CHANNEL SIGNAL DEMODULATION UNIT

1. A first terminal apparatus that communicates with a second terminalapparatus, the first terminal apparatus comprising: a CCA (Clear ChannelAssessment) unit configured to assess whether a radio resource is idleor busy, using a carrier sense based on a first threshold value andsecond threshold value; and a transmission unit configured to transmit aframe, wherein the transmission unit transmits the frame which includesPHY (Physical) header including first information associated with thecarrier sense. the first information associated with the carrier senceallowes the second terminal apparatus to use the second threshold value,and the PHY header including the second information indicatingdifference between the first threshold value and the second thresholdvalue.
 2. A communication method used for a first terminal apparatusthat communicates with a second terminal apparatus, the communicationmethod comprising the steps of: determining whether a radio resource isidle or busy, using a carrier sense; and transmitting a frame, whereinthe transmission unit transmits the frame which includes PHY (Physical)header including first information associated with the carrier sense,the first information associated with the carrier sence allowes thesecond terminal apparatus to use the second threshold value, and the PHYheader including the second information indicating difference betweenthe first threshold value and the second threshold value.